This relates generally to testing wireless electronic devices, and more particularly, to calibrating test equipment and using the calibrated test equipment to test wireless electronic devices.
Wireless electronic devices typically include transceiver circuitry, antenna circuitry, and other radio-frequency circuitry that provides wireless communications capabilities. During testing, wireless electronic devices under test (DUTs) can exhibit different performance levels. For example, each wireless DUT in a group of DUTs can exhibit its own output power level, gain, frequency response, efficiency, linearity, dynamic range, etc.
The performance of a wireless DUT can be measured using an over-the-air (OTA) test station. An OTA test station includes a test chamber having a test chamber antenna, a test unit, and a test host. The antenna is connected to the test unit and is used in sending and receiving radio-frequency (RF) signals to and from the test unit. The test host is connected to the test unit and directs the test unit to perform desired operations during testing.
During test operations, a wireless DUT is placed into the test chamber and communicates wirelessly with the antenna in the test chamber. Wireless transmissions of this type experience OTA path loss between the DUT antenna and the antenna of the test chamber.
An OTA test system typically includes multiple OTA test stations that are used to test multiple wireless DUTs in parallel. Each OTA test station typically includes its own test chamber, test unit, and test host. A production DUT is placed into the test chamber of each test station during product testing. Typical product testing involves measuring the wireless performance of each DUT and applying pass/fail criteria.
The radio-frequency path of each test station has its own unique OTA path loss characteristic. These unique path losses should be taken into account for accurate testing. Path loss characterization is sensitive to the location (placement) of the test chamber antenna within the test chamber and varies as a function of operating frequency. As a result, calibrating the path loss of a test station with a single test chamber antenna may provide inaccurate measurements as the placement of the test chamber antenna and testing conditions change over time.
It would therefore be desirable to be able to provide improved calibration techniques for calibrating OTA test systems.